I did a bit of searching and it seems like YMMV. Couldn't find specifics on Air India, but some experiences with other airlines here:

http://www.flyertalk.com/forum/conti...let-slide.html

Also, same question posted here for a different airline, some other people's experiences.

http://www.flyertalk.com/forum/air-c...-leniency.html

I once checked a suitcase that was clearly over the lxwxh requirement, but only weighed 25 pounds, and they let me through (JFK-MRS on LH). Hopefully you get someone that will let it slide.